Ultrasonic treatment to improve the quality of recycled pulp fiber

The effect of ultrasound on the quality of recycled fibers was investigated. Ultrasound was applied to recycled pulp fiber suspension before ink removal by conventional flotation. The ultrasonic treatment induced an increase in the sedimentation volume of the fiber, which implies that the flexibility and bulkiness of the fiber increase. The water retention value of the ultrasonically treated fiber recovered from the loss caused by the recycling. These facts are due to a beating effect of the treatment. The paper sheets prepared from the ultrasonically treated fiber suspension showed higher sheet density, tensile strength, and brightness than that from an untreated fiber suspension. The process, which consists of ultrasonic treatment for 1 min following flotation deinking, requires about 1.4 times as much energy as the conventional flotation deinking process, but it induced 20% improvement in brightness. The results indicate that the ultrasonic treatment is effective in improving recycled fiber quality.This report was presented in part at the 48th Annual Meeting of the Japan Wood Research Society, Shizuoka, April 1998; and at the 5th Annual Meeting of the Japan Cellulose Society, Kyoto, July 1998